Diego Stocco made this incredible thing and explain:
To determine the key I used the lowest note I could play and recorded the rest around it. Besides playing the leaves, I used bows of different sizes, a piano hammer and a paint brush. As far as microphones I used my Røde NT6, a customized stethoscope and tiny MEAS piezo transducers.
I played all the sounds and rhythms only with the bonsai, I didn't use any synthesizer or samplers to create or modify the sounds.